Re: [PATCH v4 net-next 1/4] net: core: page_pool: add user cnt preventing pool deletion

Ivan Khoronzhuk
2019-06-26T10:49:57Z

On Wed, Jun 26, 2019 at 12:42:16PM +0200, Jesper Dangaard Brouer wrote:
>On Tue, 25 Jun 2019 20:59:45 +0300
>Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org> wrote:
>
>> Add user counter allowing to delete pool only when no users.
>> It doesn't prevent pool from flush, only prevents freeing the
>> pool instance. Helps when no need to delete the pool and now
>> it's user responsibility to free it by calling page_pool_free()
>> while destroying procedure. It also makes to use page_pool_free()
>> explicitly, not fully hidden in xdp unreg, which looks more
>> correct after page pool "create" routine.
>
>No, this is wrong.
below.

>
>> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
>> ---
>> drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 8 +++++---
>> include/net/page_pool.h | 7 +++++++
>> net/core/page_pool.c | 7 +++++++
>> net/core/xdp.c | 3 +++
>> 4 files changed, 22 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> index 5e40db8f92e6..cb028de64a1d 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> @@ -545,10 +545,8 @@ static int mlx5e_alloc_rq(struct mlx5e_channel *c,
>> }
>> err = xdp_rxq_info_reg_mem_model(&rq->xdp_rxq,
>> MEM_TYPE_PAGE_POOL, rq->page_pool);
>> - if (err) {
>> - page_pool_free(rq->page_pool);
>> + if (err)
>> goto err_free;
>> - }
>>
>> for (i = 0; i < wq_sz; i++) {
>> if (rq->wq_type == MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ) {
>> @@ -613,6 +611,8 @@ static int mlx5e_alloc_rq(struct mlx5e_channel *c,
>> if (rq->xdp_prog)
>> bpf_prog_put(rq->xdp_prog);
>> xdp_rxq_info_unreg(&rq->xdp_rxq);
>> + if (rq->page_pool)
>> + page_pool_free(rq->page_pool);
>> mlx5_wq_destroy(&rq->wq_ctrl);
>>
>> return err;
>> @@ -643,6 +643,8 @@ static void mlx5e_free_rq(struct mlx5e_rq *rq)
>> }
>>
>> xdp_rxq_info_unreg(&rq->xdp_rxq);
>> + if (rq->page_pool)
>> + page_pool_free(rq->page_pool);
>
>No, this is wrong. The hole point with the merged page_pool fixes
>patchset was that page_pool_free() needs to be delayed until no-more
>in-flight packets exist.

Probably it's not so obvious, but it's still delayed and deleted only
after no-more in-flight packets exist. Here question is only who is able
to do this first based on refcnt.

>
>
>> mlx5_wq_destroy(&rq->wq_ctrl);
>> }
>>
>> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
>> index f07c518ef8a5..1ec838e9927e 100644
>> --- a/include/net/page_pool.h
>> +++ b/include/net/page_pool.h
>> @@ -101,6 +101,7 @@ struct page_pool {
>> struct ptr_ring ring;
>>
>> atomic_t pages_state_release_cnt;
>> + atomic_t user_cnt;
>> };
>>
>> struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
>> @@ -183,6 +184,12 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
>> return page->dma_addr;
>> }
>>
>> +/* used to prevent pool from deallocation */
>> +static inline void page_pool_get(struct page_pool *pool)
>> +{
>> + atomic_inc(&pool->user_cnt);
>> +}
>> +
>> static inline bool is_page_pool_compiled_in(void)
>> {
>> #ifdef CONFIG_PAGE_POOL
>> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>> index b366f59885c1..169b0e3c870e 100644
>> --- a/net/core/page_pool.c
>> +++ b/net/core/page_pool.c
>> @@ -48,6 +48,7 @@ static int page_pool_init(struct page_pool *pool,
>> return -ENOMEM;
>>
>> atomic_set(&pool->pages_state_release_cnt, 0);
>> + atomic_set(&pool->user_cnt, 0);
>>
>> if (pool->p.flags & PP_FLAG_DMA_MAP)
>> get_device(pool->p.dev);
>> @@ -70,6 +71,8 @@ struct page_pool *page_pool_create(const struct page_pool_params *params)
>> kfree(pool);
>> return ERR_PTR(err);
>> }
>> +
>> + page_pool_get(pool);
>> return pool;
>> }
>> EXPORT_SYMBOL(page_pool_create);
>> @@ -356,6 +359,10 @@ static void __warn_in_flight(struct page_pool *pool)
>>
>> void __page_pool_free(struct page_pool *pool)
>> {
>> + /* free only if no users */
>> + if (!atomic_dec_and_test(&pool->user_cnt))
>> + return;
>> +
>> WARN(pool->alloc.count, "API usage violation");
>> WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
>>
>> diff --git a/net/core/xdp.c b/net/core/xdp.c
>> index 829377cc83db..04bdcd784d2e 100644
>> --- a/net/core/xdp.c
>> +++ b/net/core/xdp.c
>> @@ -372,6 +372,9 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
>>
>> mutex_unlock(&mem_id_lock);
>>
>> + if (type == MEM_TYPE_PAGE_POOL)
>> + page_pool_get(xdp_alloc->page_pool);
>> +
>> trace_mem_connect(xdp_alloc, xdp_rxq);
>> return 0;
>> err:
>
>
>
>--
>Best regards,
> Jesper Dangaard Brouer
> MSc.CS, Principal Kernel Engineer at Red Hat
> LinkedIn: http://www.linkedin.com/in/brouer

--
Regards,
Ivan Khoronzhuk